Chainsaw bikes

Matt Barrack

Member
Joined
May 30, 2017
Messages
99
I got a guy who wants a motor on his bike and I mentioned motorized bike kits. But then he found videos of bikes with chainsaw motors on their bikes. Is a 2-stroke kit better than a chainsaw bike? I understand that a chainsaw would take more work, but in the end, which out preforms the other? These motors don't really seem too different from a chainsaw motor to me.
 


5-7HEAVEN

Well-Known Member
Joined
Jun 22, 2007
Messages
1,180
Chainsaw engines have torque to cut thru thick tree trunks.

One weak point is their small clutch.
I have not seen anyone adapting inexpensive
78mm clutches to this hardy engine-type.

This brings up its second weak point:
the ability to optimize the low gear ratio that chainsaw engines need.

That's the main reason why most chainsaw engines end up
with clutchless friction drive.

Whenever I see a chainsaw engine sprocket
directly linked to a rear wheel sprocket,

I KNOW its gear ratio isn't at its optimum.
 

Matt Barrack

Member
Joined
May 30, 2017
Messages
99
Chainsaw engines have torque to cut thru thick tree trunks.

Their weak point is their small clutch.
I have not seen anyone adapting inexpensive
78mm clutches to this hardy engine-type.

That's the main reason why most chainsaw engines end up
with clutchless friction drive.

Whenever I see a chainsaw engine sprocket
directly linked to a rear wheel sprocket,

I KNOW its gear ratio isn't at its optimum.
So, should I make it a friction drive?
 

5-7HEAVEN

Well-Known Member
Joined
Jun 22, 2007
Messages
1,180
If you want a simple install, do friction drive, with the engine firmly mounted.
Like this:
090529 Chainsaw Powered Bicycle

A more versatile friction install would have a way to lift the roller off the rear tire.
I believe it's called a gravity clutch or scissors clutch.
Then you can pedal without engine resistance.
You will also be able to turn the engine off, or idle at any time.
You'll also be able to pull start the engine.

In any case, to prevent crankshaft damage,
find a way to bearing support the friction roller's outboard edge.

Running thru gears and sprockets would work better, I think.
Like this:

Actually, this setup needs a much bigger rear wheel sprocket
and a lower gear ratio.

Good luck.
 
Last edited:

Matt Barrack

Member
Joined
May 30, 2017
Messages
99
If you want a simple install, do friction drive, with the engine firmly mounted.

A more versatile friction install would have a way to lift the roller off the rear tire.
I believe it's called a gravity clutch or scissors clutch.
Then you can pedal without engine resistance.
You will also be able to turn the engine off, or idle at any time.
You'll also be able to pull start the engine.

In any case, to prevent crankshaft damage,
find a way to bearing support the friction roller's outboard edge.

Good luck.
Thanks. Honestly, I know it's more work, but I like the sound of a chain drive more. Hopefully I can get my biggest saw on the bike.
 

5-7HEAVEN

Well-Known Member
Joined
Jun 22, 2007
Messages
1,180
I LOVE gears, especially running the power through the bike's cassette.

Just remember you'll need about 20:1 gear ratio to
spin the chainsaw engine to 10,000rpm at 39mph.

Chainsaw engines make power at high rpm.
 
Last edited:

Bonefish

Active Member
Joined
Jun 14, 2009
Messages
560
Hey 5-7, you got a link to your latest build? I have moved on to scooters since procedure RS-68 was introduced in Florida.
 

Matt Barrack

Member
Joined
May 30, 2017
Messages
99
I LOVE gears, especially running the power through the bike's cassette.

Just remember you'll need about 20:1 gear ratio to
spin the chainsaw engine to 10,000rpm at 39mph.

Chainsaw engines make power at high rpm.
Alright thanks. Just to be clear, that means that the gear on the engine needs to be 20x smaller than the one on the bike?
 
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